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Can We Prevent ACL Injuries? (Part II)

As I discussed in the first part of this article series, ACL injuries are the most-feared injury in lacrosse because they end the athlete’s season.

Just to quickly review, a complete tear of the ACL (anterior cruciate ligament) in the knee is a season-ending injury that requires surgery to repair the key ligament (which effectively stabilizes the knee joint).

The big question today is how do we prevent this injury from occurring? Can we actually prevent this injury?

That’s the million-dollar question.

Before we cover how to prevent this, we have to understand why this injury happens in the first place.

Many lacrosse coaches I’ve spoken with have said that to help prevent ACL injuries, the athlete needs “knee strength.”

Well, that’s sort of true but what exactly does that mean?

It’s more than knee strength and we have to understand the components of that.

According to landmark published research by Hewett (1), there are 4 major reasons that ACL injuries happen.

These 4 factors are *neuromuscular that contribute to the mechanism of injury (seen below) where the upper and lower leg are displaced in an awkward and stressful position (*by neuromuscular, we mean that there are things that can be trained to correct muscle imbalances and weakness to improve performance).

Here are the four most common components that occur.

1-LIGAMENT DOMINANCE

Ligament dominance means there is muscle weakness that is not trained to absorb and respond to forces on the field of play.

Therefore the ligaments are the dominant “force absorber” in knee stress – such as with the valgus position pictured above.

Remember this point.

The ability to produce and absorb forces are absolutely key in preventing these injuries.

The ability to produce and absorb forces are absolutely key in preventing these injuries.

Think of weak muscles or poorly controlled lower extremity muscles that don’t respond well during running, cutting, or jumping.

The muscles groups in the lower extremities simply aren’t able to absorb the ground reaction force (GRF).

In simple terms and without covering physics and the laws of force, you need a certain amount of strength to react against the ground (GRF).

When you don’t have sufficient strength, it’s an accident waiting to happen.

This is because your muscles don’t absorb those ground reaction forces enough.

As a result, more stress is placed on the ACL during cutting and planting (as in lacrosse).

Needless to say, muscle strength and control is extremely important here to prevent ACL disruption.

SOLUTIONS: Neuromuscular training and increased focus on technique and mechanics.

(*NOTE: We will cover specific training approaches in much more detail in the next installment of this article series).

2-QUADRICEPS DOMINANCE

This is essentially muscle imbalance between the quadriceps and hamstrings (and posterior chain muscles).

Females, in particular, preferentially use their quadriceps muscles.

This can mean weak or disproportionate use of the hamstrings muscle group.

Since the hamstrings are considered synergistic with the ACL, hamstring strengthening can potentially be more of a focus to reduce the risk of injury. But not just the hamstrings, the entire posterior chain.

Since females are highly quad dominant, an emphasis should be placed on the strengthening of the posterior chain.

SOLUTIONS: Emphasis on posterior chain development to negate muscle imbalance – all muscles in the posterior chain such as hamstrings, glutes, abductor muscles calves and more, trained concentrically, eccentrically, and isometrically. 

3-LEG DOMINANCE

This is the use of one leg – or favoring one leg – over the other.

This could be considered a gross asymmetry where one leg is significantly stronger or more dominant than the other.

While it it common to have one side stronger (think of your dominant hand versus your non-dominant hand), we want to narrow the gap as much as possible to have more symmetry between one side versus the other.

Think of lacrosse specifically, what do we work on a lot when it come to stick work?

Being ambidextrous (where both the right and left are able to be used equally well).

ACL injury is often when bodyweight is on a single leg.

Is there a preferred plant leg or lead leg?

Having large degrees of leg asymmetry may have greater potential for injury.

As with balance with the quads and hamstrings, we want balance between one leg and the other so this is not so much asymmetry.

SOLUTIONS: Single leg exercises that work on each leg independently – to help correct any large gap in lower extremity asymmetry.

4-TRUNK DOMINANCE (or CORE DYSFUNCTION)

Finally, we have one component that may be surprising but having poor trunk strength and control is actually a risk factor for ACL injury.

This is the inability to precisely control the trunk in 3-dimensional space.

Think of “weak abs” or weak trunk and back muscles.

You might be thinking, why is this important when it comes to ACL injuries?

When running, it is critical to control the trunk and maintain “stiffness” of the core.

If the trunk is weak and not able to remain stiff and controlled during high speed running, this places increased stress on the lower body and, specifically, the ACL because of the increased force absorption to compensate for the weakness.

Think of the trunk excessively bending or rotating while running, this would place more stress the the lower body.

Again, weakness in one area demands more of the lower body and, ultimately, increases the stress on the ACL.

I hope this make sense.

SOLUTIONS: Core/trunk strengthening and control exercises.


I want to summarize and simplify these 4 contributing factors to ACL injury:

  • MUSCLE WEAKNESS (in the legs)
  • MUSCLE IMBALANCE (quads to hams/posterior chain)
  • STRONG LEG/WEAK LEG (large asymmetry between each leg)
  • WEAK CORE/TRUNK

Notice that all of these are “trainable” and can be addressed with appropriate performance training.

Now that you know why ACL tears can happen (from a neuromuscular standpoint), let’s quickly summarize how to help prevent them.

  • Address muscle imbalances
  • Address muscle weakness
  • Provide proper technique and bio-mechanical training
  • Athlete (and coach) education
  • Proper neuromuscular training
  • Intelligent program design
  • Athlete assessment and screening for risk factors

Listed above are the primary factors in ACL injury, but there are more.

There are non-modifiable factors (things that cannot be trained or changed) such as:

  • Gender (Female > Male)
  • Anatomic/structural variations (wide pelvis structure, anatomical differences in knee, natural valgus (knee-in) component)
  • Family history of ACL injury
  • Previous history of ACL injury (we could suggest there are modifiable components to this)
  • Hormonal influences (menstrual cycle and hormonal fluctuations that are non-modifiable)

Other contributing factors (that can be modified):

  • Shoe type (cleats that are not “too aggressive” for the respective surface, there is data on this)
  • Surface (grass vs turf)

As you can see, there are several things that contribute to ACL tears.

What we can do to prevent ACL tears is to focus on the modifiable components to effectively train and help reduce the risk of injury.

It’s fair to say that we cannot 100% prevent an ACL injury but we can certainly do the right things to significantly reduce the likelihood of this injury.

It’s fair to say that we cannot 100% prevent an ACL injury but we can certainly do the right things to significantly reduce the likelihood of this injury. 


In the next article of this series, we’ll cover the specific strategies to prevent these injuries for healthier, stronger, more durable lacrosse athletes.


CITATIONS:

(1)  Hewett TE, Ford KR, Hoogenboom BJ, Myer GD. Understanding and preventing acl injuries: current biomechanical and epidemiologic considerations – update 2010. N Am J Sports Phys Ther. 2010 Dec;5(4):234-51.

Coach Scott

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